Iron-Catalyzed Stereoconvergent 1,4-Hydrosilylation of Conjugated Dienes

Stereoconvergent transformation of E/Z mixtures of olefins to products with a single steric configuration is of great practical importance but hard to achieve. Herein, we report an iron-catalyzed stereoconvergent 1,4-hydrosilylation reactions of E/Z mixtures of readily available conjugated dienes for the synthesis of Z-allylsilanes with high regioselectivity and exclusive stereoselectivity. Mechanistic studies suggest that the reactions most likely proceed through a two-electron redox mechanism. The stereoselectivity of the reactions is ultimately determined by the crowded reaction cavity of the alpha-diimine ligand-modified iron catalyst, which forces the conjugated diene to coordinate with the iron center in a cis conformation, which in turn results in generation of an anti-pi-allyl iron intermediate. The mechanism of this stereoconvergent transformation differs from previously reported mechanisms of other related reactions involving radicals or metal-hydride species. An iron-catalyzed stereoconvergent 1,4-hydrosilylation reaction enables the highly effective synthesis of Z-allylsilanes from easily available E/Z mixtures of conjugated dienes.image